1. Field of the Invention
The present invention relates generally to a cooling device for use in an image forming apparatus, such as a printer, a facsimile, and a copying machine, and to an image forming apparatus that includes the cooling device.
2. Description of the Related Art
It is known that in a typical image forming apparatus, devices, such as an optical writing device, fixing device, or a developing device, provided in the image forming apparatus produce heat and increase the temperature in the devices.
For instance, in the developing device, when a developer-agitating-and-conveying member that agitates and conveys a developer in the developing device is driven, frictional heat produced by friction between the developer-agitating-and-conveying member and the developer and friction among developing agent particles increases the temperature in the device. In addition, frictional heat produced by friction between the developer and a developer regulating member that regulates the thickness of the developer applied onto a developer carrier prior to conveyance of the developer to a developing area and frictional heat produced by friction among developer particles when the developer is subjected to regulation performed by the developer regulating member increase the temperature in the developing device.
The rise in temperature can fuse toner, causing the toner to stick to the developer regulating member, the developer carrier, the image carrier, and the like; this can result in a defective image, such as a streaked image. Even when the toner is not heated to a temperature at which the toner is fused, application of a pressure, friction, or the like stress to the toner can cause surface additive on the surface of the toner to be embedded into the toner or come off from the surface of the toner; this can disadvantageously cause toner component to stick to surfaces of carrier particles. Due to the disadvantage, developing performance can become less reliable from a long-term viewpoint. In particular, when toner of relatively low fusing temperature is used in order to reduce energy required for image fixation, as is often in recent years, defective image is more likely to be produced because of sticking of the toner.
Image forming apparatus that includes, to overcome such a disadvantage, a cooling device of an air cooling type that conveys air taken in from the outside by an air-cooling fan to an area around a developing device through a duct and produces an air flow that cools the developing device to thereby prevent excessive rise in temperature in the developing device has conventionally been known. However, in recent years, less and less extra space is left around a developing device because packaging inside image forming apparatuses is becoming denser because of recent compact design. This has made it difficult to find space for arranging a duct for conveying flow of air taken in by the air-cooling fan to an area around a developing device. Hence, it has become difficult to perform forced-air cooling of the developing device.
An image forming apparatus that includes a cooling device of a liquid cooling type that cools a developing device by circulating liquid is disclosed in Japanese Patent Laid-open Publication No. 2008-277684. The cooling device of the liquid cooling type includes: a heat receiving unit arranged in contact with a wall surface of the developing device and in which coolant receives heat from the developing device; a heat radiating unit for radiating the heat from the coolant; a circulating pipe that is arranged such that the coolant circulates through the heat receiving unit and the heat radiating unit; and a conveying unit that conveys the coolant in the circulating pipe. The cooling device of the liquid cooling type is capable of cooling more efficiently than an air-cooling cooling device, and hence capable of cooling the developing device efficiently. The circulating pipe can be arranged around a developing device even when space around the developing device is relatively small because cross-sectional profile of the circulating pipe, thorough which coolant circulates, is smaller than that of a duct. Thus, the cooling device is capable of cooling a developing device even when packaging inside an image forming apparatus is dense.
The image forming apparatus disclosed in Japanese Patent Laid-open Publication No. 2008-277684 includes a heat conductive member for improving heat conduction from the developing device to the heat receiving unit so that heat is conducted from the developing device to the heat receiving unit through the heat conductive member. The developing device is detachably attached to the image forming apparatus. The heat receiving unit is to be separated from the developing device when the developing device is detached from the image forming apparatus, whereas the heat receiving unit is to be brought into contact with the developing device when the developing device is attached to a main body of the image forming apparatus. To protect the heat conductive member from being peeled off or torn due to repeated contacts between the heat receiving unit and the developing device, a protection member that protects the heat conductive member is disposed on the heat conductive member.
There can be cases where separating the heat receiving unit from an object to be cooled (hereinafter, “cooling target”) externally exposes a surface of the protection member to the outside, causing toner having been scattered in the image forming apparatus to stick to the surface of the protection member. In this case, binder resin of the toner may be bonded to the protection member which is compatible with the binder toner in a compatible state, which can degrade the protection member, thereby degrading capability of the protection member to protect the heat conductive member.
The present invention has been conceived in view of the above circumstance and aims at providing a cooling device capable of retarding degradation of a protection member resulting from sticking of toner to the protection member, thereby maintaining capability of the protection member to protect a heat conductive member and an image forming apparatus that includes the cooling device.